Synthesis of 3,4-dihydropyrimidin-2(1H)-ones catalyzed by poly(ferric 2-acrylamido-2-methylpropanesulfonate)

Article abstract of DOI:10.1007/s11696-020-01327-7

Poly(ferric 2-acrylamido-2-methylpropanesulfonate) (PFAMPS) was prepared via the reaction of poly(2-acrylamido-2-methylpropanesulfonic acid) and Fe(OH)₃. PFAMPS was used as a heterogeneous catalyst for the Biginelli reaction of aldehyde, ethyl

Full text of DOI:10.1007/s11696-020-01327-7

Chemical Papers
https://doi.org/10.1007/s11696-020-01327-7
ORIGINAL PAPER
Synthesis of 3,4‑dihydropyrimidin‑2(1H)‑ones catalyzed by poly(ferric
2‑acrylamido‑2‑methylpropanesulfonate)
Zhihao Zhao1 · Hongguang Dai1 · Lan Shi1
Received: 28 May 2020 / Accepted: 17 August 2020
© Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract
Poly(ferric 2-acrylamido-2-methylpropanesulfonate) (PFAMPS) was prepared via the reaction of poly(2-acrylamido-2-meth-
ylpropanesulfonic acid) and Fe(OH)3. PFAMPS was used as a heterogeneous catalyst for the Biginelli reaction of aldehyde,
ethyl acetoacetate, and urea to synthesize 3,4-dihydropyrimidin-2(1H)-ones with yields of 70–87%. PFAMPS can be recy-
cled six times without signifcant loss in catalytic activity. For comparison, ferric lignosulfonate (FLSA), ferric cellulose
sulfonate (FCSA), ferric starch sulfonate (FSSA), and ferric 732 cation exchange resin (FACER) were used as catalysts of
the Biginelli reaction. It was shown that the catalytic activities of recycled FLSA, FCSA, FSSA, and FACER signifcantly
decreased after two reactions. Fe3+ in the polymer sulfonates acted as the catalyst for the Biginelli reaction. PFAMPS was
the chelate, where the action between Fe3+ and the poly(2-acrylamido-2-methylpropanesulfonate) matrix was strong, and
Fe3+ lost little from the PFAMPS. However, signifcant Fe3+ loss was observed in the FLSA, FCSA, FSSA and FACER
polymer matrices after reuse.
Keywords Biginelli reaction · Catalyst · Poly(ferric 2-acrylamido-2-methylpropanesulfonate) · Synthesis
Introduction
MCM-41 (Tayebee and Ghadamgahi 2017), phosphotung-
stic acid grafted zeolite imidazolate (Tayebee et al. 2019),
Fe3O4@meglumine sulfonic acid (Moradi and Tadayon
2018), sulfated graphene and graphene oxide (Vessally
et al. 2017), ionic liquid 1,3-disulfonic acid benzimidazo-
lium chloride (Abbasi 2016), Pb/Cu (Mathur et al. 2018),
Fe+3-montmorillonite K10 (Fekri et al. 2017), Co@imine-
Na+-MMT (Khorshidi et al. 2017), metal-supported nano-
catalyst Fe–Cu/ZSM-5 (Safa et al. 2015), KF-modifed clay
(Bentahar et al. 2019), aluminium-planted mesoporous silica
(Murata et al. 2010), FeCl3-supported nanopore silica (Ahn
et al. 2008), and polycarbosilanes containing Cu(II) (Man-
gala and Sreekumar 2019). Some catalysts are expensive,
toxic, and non-recyclable. Although some recyclable solid
organic and inorganic acids were invented as catalysts for
the Biginelli reaction, there are still many drawbacks. Silica
solid acids as catalysts for the Biginelli reaction have been
studied, but the Brunauer–Emmett–Teller (BET) surface
greatly infuences catalytic activity, and the process for pre-
paring porous silica catalysts is complex (Cheng et al. 2014).
The catalytic activity of some recycled catalysts decreases
signifcantly (Moradi and Tadayon 2018). It is necessary to
study the reason why the catalytic activity decreases with
increasing numbers of catalytic cycles. Typically, there are
3,4-Dihydropyrimidin-2(1H)-ones exhibit biological and
pharmacological activities, and are widely used as calcium
channel antagonists, anti-bacterial, anti-hypertensive, and
anti-infammatory agents (Tayebee and Ghadamgahi 2017).
In 1893, Pietro Biginelli (1893) frst reported the synthe-
sis of 3,4-dihydropyrimidin-2(1H)-one (DHPM) by a sim-
ple one-pot condensation reaction of aromatic aldehydes,
β-ketoesters and urea under strongly acidic conditions (Taye-
bee and Ghadamgahi 2017). In recent decades, a number of
catalysts for the Biginelli reaction were studied by research-
ers, such as calix[8]arene sulfonic acid (An et al. 2016),
phthalic acid (Mohamadpour et al. 2018), zirconium(IV)
4-sulphophenylethyliminobismethylphosphonate (Yang et al.
2011), gallium(III) trifate (Li et al. 2010), Co(NO3)2 (Nasr-
Esfahani et al. 2014), iron(III) tosylate (Starcevich et al.
2013), 3-[(3-(trimethoxysilyl)propyl)thio]propane-1-oxy-
sulfonic acid (Jetti et al. 2017), mesoporous NH4H2PO4/
* Hongguang Dai
imaudm@imau.edu.cn
1
College of Science, Inner Mongolia Agricultural University,
Hohhot 010018, People’s Republic of China
Vol.:(0123456789)
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Chemical Papers
Table 1 Preparation of PAMPS
still some drawbacks for the reported catalysts, and it has
become necessary to explore new catalysts for the Biginelli
reaction.
Entry
PAMPS
AMPS/g
MBA/g
(NH4)2S2O8/g
1
2
3
4
5
PAMPS5M
PAMPS10M
PAMPS15M
PAMPS20M
PAMPS25M
10
10
10
10
10
0.5
1
1.5
2
0.03
0.03
0.03
0.03
0.03
Iron ions are nontoxic Lewis acids, and used extensively
as catalysts. Generally, iron salts as catalysts are difcult
to be recycled, so ionic iron compounds must be supported
on inorganic materials or polymers for catalysis (Shi et al.
2018). However, significant iron ion losses occur with
increasing numbers of recycle loops, and catalytic efects
decrease. There are amido and sulfonic groups in poly(2-
acrylamido-2-methylpropanesulfonic acid) (PAMPS), which
can be used as the chelant of the metal ions (Zhang et al.
2007). PAMPS is extensively used as a superabsorbent, elec-
trolyte for batteries (Cui and Tang 2012), a catalyst (Yin
et al. 2014), or catalyst supporter (Asadi et al. 2017). In this
manuscript, PAMPS was prepared by free-radical polym-
erization using 2-acrylamido-2-methylpropanesulfonic acid
as the monomer and N,N’-methylenebisacrylamide as the
crosslinking agent. Poly(ferric 2-acrylamido-2-methylpro-
panesulfonate) (PFAMPS) was obtained by the reaction of
PAMPS and ferric hydroxide. 3,4-Dihydropyrimidin-2(1H)-
ones were synthesized by the Biginelli reaction catalyzed by
PFAMPS, which is recyclable. For comparison, ferric ligno-
sulfonate (FLSA), ferric cellulose sulfonate (FCSA), ferric
starch sulfonate (FSSA), and ferric 732 cation exchange resin
(FACER) were used as catalysts for the Biginelli reaction.
2.5
H2
C
H
C
CH
*
*
H2C
n
O C
NH
H3C C CH3
H2C
O C
NH
H3C C CH3
H2C
(NH4)2S2O8
70 oC
SO3H
SO3H
Scheme 1. Synthesis of PAMPS
induced at 70 °C using 0.03 g ammonium persulfate as the
free-radical initiator. After 6 h, PAMPS gel was obtained.
The PAMPS gel was soaked in distilled water and fltered to
remove impurities. Finally, PAMPS was dried in an oven at
70 °C until the weight was unchanged. PAMPS was ground
and sieved to obtain 0.25–1 mm particles. The reaction equa-
tion is shown in Scheme 1.
Experimental
Synthesis of poly(ferric
2‑acrylamido‑2‑methylpropanesulfonate) (PFAMPS)
Chemicals and measurements
Analytical grades of 2-acrylamido-2-methylpropane sul-
fonic acid (AMPS), N,N’-methylenebisacrylamide (MBA),
ammonium persulfate, aromatic aldehyde, ethyl acetoac-
etate, urea, starch, cellulose, 732 cation exchange resin and
sodium lignosulfonate were commercially purchased from
Tianjin Chemical Reagent Ltd.
PAMPS5M and stoichiometric Fe(OH)3 in ethanol were
stirred for 8 h at 50 °C and then fltered. Acetic acid was
added to the mixtures to neutralize the unreacted Fe(OH)3,
and then PFAMPS was fltered and rinsed with ethanol.
PFAMPS was dried at 70 °C until the weight was unchanged.
Fourier-transform infrared (FT-IR) spectra of PFAMPS
were acquired with a Spectrum 65 Infrared spectrum scanner
(PerkinElmer, USA) in refection mode.
Synthesis of other polymer sulfonic acids and ferric
polymer sulfonate
1H NMR spectra were determined by a BioSpin GmbH
600 M NMR spectrometer (Bruker, Switzerland) with TMS
as the internal standard and DMSO as the solvent.
Cellulose sulfonic acid (CSA) and starch sulfonic acid (SSA)
were synthesized according to Vekariya and Patel 2015.
Lignosulfonic acid (LSA) and acidic 732 cation exchange
resin (ACER) were prepared according to Dai et al. 2018.
FLSA, FCSA, FSSA, and FACER were synthesized in a
similar way as PFAMPS.
Synthesis of PAMPS and PFAMPS
According to a reported method (Cui and Tang 2012),
PAMPS was synthesized by free-radical polymerization.
First, 10 g monomer AMPS and crosslinking agent MBA
(as shown in Table 1), were dissolved in 90 mL of H2O,
the solution was deoxygenated by bubbling pure nitrogen
for 0.5 h, and the polymerization reaction was thermally
Synthesis of 3,4‑dihydropyrimidin‑2(1H)‑ones
Aldehyde (5 mmol), urea (or thiourea) (7.5 mmol), ethyl
acetoacetate (5 mmol, 650 mg), and the catalyst in ethanol
(5 mL) were heated under refux (Scheme 2). The catalyst
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Chemical Papers
Scheme 2. Synthesis of
3,4-dihydropyrimidin-2(1H)-
ones
was separated from the solution by fltering. The catalyst was
washed with hot ethanol (5 mL×2), the hot ethanol solution
was combined with the mixtures, and the solvent was evapo-
rated under reduced pressure. The solid was recrystallized
from ethanol to give a pure product. The catalyst was dried
at 70 °C for reuse.
ammonia and acetic acid. Then, 10 mL ammonia and ammo-
nium acetate bufer solution were added, and four drops of
xylenol orange were added as the indicator. The solution was
titrated with standard zinc solution to purple red as the end
point. The Fe3+ density of the catalyst was calculated using
the equation below:
5-ethoxycarbonyl-6-methyl-4-(4-methoxyphenyl)-3,4-di-
hydropyrimidin-2(1H)-one (4b) Crystalline solid, m.p.:
205–208 °C; 1H NMR (600 MHz, DMSO) δ 9.15 (s, 1H),
7.66 (s, 1H), 7.15–7.14 (m, 2H), 6.89–6.87 (m, 2H), 5.09 (d,
J=3.0 Hz, 1H), 3.98 (q, J=7.2 Hz, 2H), 3.72 (s, 3H), 2.24
(s, 3H), 1.11 (t, J=7.2 Hz, 3H).
15 × c1 − c2v2
Fe3+density =
(2)
w
where c1 is the concentration of EDTA, c2 is the concentra-
tion of Zn2+, v2 is the volume of Zn2+ solution, and w is the
weight of dried catalyst used in the titration.
5-ethoxycarbonyl-6-methyl-4-(4-methoxyphenyl)-3,4-di-
hydropyrimidin-2(1H)-thione (4j) Crystalline solid, m.p.:
150–152 °C; 1H NMR (600 MHz, DMSO) δ 10.29 (s, 1H),
9.60 (s, 1H), 7.14–7.12 (m, 2H), 6.92–6.89 (m, 2H), 5.12 (d,
J=6 Hz, 1H), 4.01 (q, J=7.2 Hz, 2H), 3.73 (s, 3H), 2.29 (s,
3H), 1.11 (t, J=7.2 Hz, 3H).
Results and discussion
FT‑IR
As shown in Fig. 1, of the FT-IR of PAMPS5M, the peak at
1639 cm−1 is ascribed to the C=O stretching vibration. The
peak at 2922 cm−1 is ascribed to saturated C–H stretching.
The peaks of O–H and N–H are all shown to be greater than
3000 cm−1. Peaks’ wavenumbers of 1216 and 1039 cm−1 are
characteristic peaks of -SO3H.
Determination of H+ density of the catalyst
H+ density of the catalyst was determined using acid–base
back titration. Approximately 30 mg of the catalyst was
soaked in 10 mL water, and 0.1 mol/L NaOH solution
(10.00 mL) was added to react with the samples for 12 h
for neutralization. An excess amount of sodium hydroxide
was then titrated against hydrochloric acid (0.1 mol/L). The
H+ density of the catalyst was calculated using the equation
below:
Recycled PFAMPS
(
)
H+density = Vb − Va × c∕w
3318
2976
(1)
1646
PFAMPS
1032
1148
where Vb is the volume of HCl used for the back titration in
the absence of the sample, Va is the volume of HCl used in
the presence of the sample, C is the concentration of HCl,
and w is the weight of dried sample used in the titration. The
experiments were carried out in triplicate, and an average
value was obtained.
2976
3318
1032
1646
1148
PAMPS5M
1039
1216
2922
3440
3000
1639
Determination of Fe3+ density of the catalyst
The Fe3+ density of the catalyst was determined using
EDTA back titration (Khalifa and Ismail 1969). 30 mg of
the catalyst was reacted with 15 mL EDTA standard solution
for 12 h. The pH of the solution was adjusted to six using
4000
3500
2500
2000
1500
1000
Wavenumber (cm-1)
Fig. 1 FT-IR of PAMPS and PFAMPS
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Chemical Papers
Compared with the FT-IR of PAMPS5M, the peak at
3318 cm−1 of PFAMPS, ascribed to N–H stretching, is
weaker, because –SO3H was displaced by (–SO3)3Fe. The
peak at 2976 cm−1 is ascribed to saturated C–H stretching,
the peak at 1646 cm−1 is ascribed to C=O stretching, and
the peaks at 1032 and 1148 cm−1 are indicative of the pres-
The influence of PAMPS with different crosslink-
ing degrees on the reaction was studied. PAMPS5M,
PAMPS10M, PAMPS15M, PAMPS20M, and PAMPS25M
were used as catalysts for the reaction, where the yields of
4a were 95, 90, 88, 83, and 83%, respectively. With increas-
ing crosslinking degrees of PAMPS, the H+ content and the
yields of 4a decreased. There was not a sulfonic group in
the crosslinking reagent MBA, so the H+ content of PAMPS
decreased with increasing crosslinking degrees.
−
ence of –SO3 .
The FT-IR of recycled PFAMPS is similar to that of vir-
gin PFAMPS, which confrms that the structure of PFAMPS
does not change after reaction catalysis. Therefore, the
catalytic efect of recycled PAMPS does not signifcantly
decrease.
As shown in Table 3, with increased PAMPS5M amounts
and reaction times, the yields of 4a increased. PAMPS could
catalyze the Biginelli reaction to synthesize 3,4-dihydropy-
rimidin-2(1H)-ones, where ionized H+ from PAMPS acted
as a catalyst. Additionally, protonic acid could act as an acid,
and Lewis acids could act catalysts. Lewis acidic Fe3+ is
widely used as a catalyst and is nontoxic, but inorganic fer-
ric salts, for example FeCl3, used as catalysts are generally
unable to be recycled. Fe3+ could be supported on inorganic
materials or polymers, and recycled after reaction catalysis,
but Fe3+ can be easily lost after recycling for some supported
Fe3+ catalysts and the catalytic efects of recycled catalysts
decrease. The reason may be that the action between Fe3+
and matrix is weak. There are amido and sulfonic groups in
PAMPS that can be used as chelants for metal ions (Wang
et al. 2009). PAMPS reacts with Fe(OH)3 to give PFAMPS,
and the action between Fe3+ and the polymer matrix is
strong. Fe3+ was not easily lost in the PAMPS matrix. In the
manuscript, PAMPS5M was chosen to react with Fe(OH)3 to
prepare PFAMPS, which was subsequently used as a catalyst
for the Biginelli reaction. As shown in Table 3, when the
amounts of PFAMPS catalyzing the reaction for 5 h were
60, 80, and 100 mg, the yields of 4a were 76, 85, and 87%,
respectively. As the amount of PFAMPS increased, the yield
of 4a increased.
The infuence of catalysts on the yield of 4a
The infuence of catalysts containing sulfonic groups on
the yield of 4a was examined. As shown in Table 2, the
Biginelli reaction of benzaldehyde (1a), ethyl acetoacetate,
and urea without catalyst yielded 4a less than 5%. The H+
densities of PAMPS5M, p-TsOH·H2O, sulfamic acid, LSA,
CSA, SSA, and ACER were 4.51, 5.26, 10.30, 2.20, 5.17,
4.39, and 0.82 mmol/g, respectively. They were each used as
catalysts to synthesize 4a. To compare the catalytic efects
of diferent catalysts, appropriate amounts of each catalyst
were added to give the same H+ contents. The yields of 4a
catalyzed by PAMPS5M, p-TsOH·H2O, sulfamic acid, LSA,
CSA, SSA, and ACER were 95, 93, 91, 80, 90, 87, and 83%,
respectively. As shown, the catalytic efect of PAMPS5M
was the best. The experiments also showed that p-TsOH·H2O
and sulfamic acid cannot be recycled as catalysts. ACER is a
traditional catalyst widely used in industry, and the amount
of ACER is 5.5 times that of PAMPS5M. The yield of 4a
catalyzed by ACER is lower than that of 4a catalyzed by
PAMPS5M.
For comparison, other sulfonic acid-type polymers,
such as LSA, CSA, SSA, and ACER, were reacted with
Table 2 Efects of various sulfonic acid-type catalysts on 4a
Entry Catalyst
H+ density
of catalyst/
mmol·g−1
Amount of Reac-
Yield/%
catalyst/
mg
tion
Table 3 Optimization of reaction conditions
time /h
Entry
Catalyst
Amount of
catalyst/mg
Reaction Yield of 4a/%
time/h
1
2
3
4
5
6
7
8
Catalyst free
PAMPS5M 4.51
PAMPS10M 4.01
PAMPS15M 3.97
PAMPS20M 3.86
PAMSP25M 3.62
p-TsOH·H2O 5.26
–
0
100
100
100
100
100
85
5
5
5
5
5
5
5
5
<5
95
90
88
83
83
93
91
1
2
3
4
5
6
7
8
PAMPS5M
PAMPS5M
PAMPS5M
PAMPS5M
PAMPS5M
PAMPS5M
PFAMPS
PFAMPS
PFAMPS
PFAMPS
PFAMPS
100
80
60
100
100
100
100
80
5
5
5
4
3
2
5
5
5
4
3
95
89
80
94
90
81
87
85
76
86
73
Sulfamic
10.30
45
acid
9
LSA
CSA
SSA
2.20
5.17
4.39
0.82
240
100
100
550
5
5
5
5
80
90
87
83
9
10
11
60
80
80
10
11
12
ACER
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Chemical Papers
Table 4 Fe3+ density of polymer-supported Fe3+
matrix acted as the catalyst for the Biginelli reaction.
There are sulfonic groups in FLSA, FACER, FCSA, and
FSSA, but there are sulfonic groups and amido groups in
PFAMPS. A complex was formed between Fe3+ and the
sulfonic and amido groups in PFAMPS, and the complex
was stable (Zhang et al. 2007). Complexes between Fe3+
and LSA, ACER, CSA, and SSA were also formed, but
the stabilities of the complexes were inferior to that of
PFAMPS.
Entry
Catalyst
Fe3+ density /
Fe3+ density of
recycled catalyst /
mmol·g−1
mmol·g−1
1
2
3
4
5
PFAMPS
FLSA
FACER
FCSA
1.37
0.57
0.20
1.39
1.41
1.23
0.24
0.041
0.62
–
FSSA
As shown in Table 6, the catalytic efciency of PFAMPS
was compared with other catalysts in the synthesis of 4a.
PFAMPS catalytic system reacted faster compared with
other catalysts.
Table 5 The infuence of polymer-supported Fe3+ on the yield of 4a
As shown in Table 7, the Biginelli reaction catalyzed by
PFAMPS gave 3,4-dihydropyrimidin-2(1H)-ones in good
yields. According to Fekri et al. 2017, Lewis acids can act as
catalysts in the Biginelli reaction, and the Fe3+ ionized from
PFAMPS acted as the catalyst. The reaction mechanism is
shown in Scheme 3 (Khorshidi et al. 2017). The reaction
proceeded through acylimine formation between aldehyde
and urea in the presence of Fe3+. Subsequently, enolate of
ethyl acetoacetate was added to the acylimine, and then
cyclodehydration occurred to aford 3,4-dihydropyrimidin-
2(1H)-ones (Fekri et al. 2017).
Entry
Catalyst
Amount of
catalyst/mg
Yield of 4a /%
1 cycle
2 cycle
3 cycle
1
2
3
4
5
PFAMPS
FLSA
FACER
FCSA
100
240
700
100
100
87
80
85
80
83
86
73
77
67
–
86
67
69
–
FSSA
–
Fe(OH)3 to prepare corresponding ferric sulfonate of poly-
mers, FLSA, FCSA, FSSA, and FACER. Their Fe3+ densi-
ties were determined and shown in Table 4. For compari-
son, when PFAMPS, FLSA, FACER, FCSA, and FSSA
were used as catalysts, respectively, their Fe3+ amounts
were the same. As shown in Table 5, the yields of 4a were
87, 80, 85, 80, and 83%, respectively. Among the catalysts,
the catalytic efect of PFAMPS was the best. Addition-
ally, the reusability of catalyst was examined, as shown in
Table 5, and with increased number of cycles, the catalytic
efects of PFAMPS did not decrease, while the catalytic
efects of other catalysts signifcantly decreased. PFAMPS
is able to be recycled six times as a catalyst, and the yields
of 4a after each successive cycle were 87, 86, 86, 86, 84,
and 84%, respectively. As shown in Table 4, after recy-
cling, little Fe3+ was lost from PFAMPS, but signifcant
losses of Fe3+ were observed from FLSA, FACER, FCSA,
and FSSA, where the ionized Fe3+ from the polymer
Conclusion
PFAMPS was prepared and used as the catalyst for the
Biginelli reaction to synthesize 3,4-dihydropyrimidin-
2(1H)-ones in good yields. PFAMPS can be reused with-
out signifcant decreases in catalytic efect. For compari-
son, ferric lignosulfonate, ferric cellulose sulfonate, ferric
starch sulfonate, and ferric 732 cation exchange resin were
used as catalysts of the Biginelli reaction. Each of these
catalysts can be reused, but their catalytic effects sig-
nifcantly decrease after reuse and Fe3+ was signifcantly
lost from the polymer matrix after reuse. A chelate of
Fe3+ and poly(2-acrylamido-2-methylpropanesulfonate)
matrix was formed, where the action between Fe3+ and
Table 6 Comparison of the
Entry Catalyst
Conditions
Reaction Yield/%
time/h
efciency of PFAMPS with that
of other reported catalysts in the
synthesis of 4a
1
2
3
4
Fe3O4@mesoporous SBA-15 (Mondal et al. 2012) EtOH/60 °C
Al-M41 (Murata et al. 2010)
[Al(H2O)6](BF4)3 (Litvic et al. 2010)
6
10
20
6
85
94
81
72
Octane/115 °C
CH3CN/Refux
Solvent free/100 °C
NH4H2PO4/MCM-41 (Tayebee and Ghadamgahi
2017)
5
6
Nano ZnO (Tamaddon and Moradi 2013)
PFAMPS (This work)
Solvent free/60 °C
EtOH/Refux
10
5
95
87
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Chemical Papers
Table 7 Synthesis of
3,4-dihydropyrimidin-2(1H)-
ones/thiones catalyzed by
PFAMPSa
Entry
R
X
Yield /%
m.p./℃
Found
Reported
4a
4b
4c
4d
4e
4f
4g
4h
4i
C6H5
O
O
O
O
O
O
O
O
S
87
82
76
80
79
74
80
81
83
80
70
75
201–203
205–208
208–210
210–211
175–177
203–205
221–223
215–217
208–209
150–152
188–190
197–199
200–202 (Mohamadpour et al. 2018)
200–202 (Tayebee and Ghadamgahi 2017)
207–209 (Moradi and Tadayon 2018)
210–213 (Vessally et al. 2017)
176–178 (Mohamadpour et al. 2018)
204–206 (Kuraitheerthakumaran et al. 2016)
220–222 (Tayebee and Ghadamgahi 2017)
215–217 (Vessally et al. 2017)
208–210 (Jetti et al. 2017)
154–156 (Jetti et al. 2017)
188–189 (Fekri et al. 2017)
196–198 (Kuraitheerthakumaran et al. 2016)
4-CH3OC6H4
4-NO2C6H4
4-ClC6H4
4-FC6H4
2-NO2C6H4
2-ClC6H4
4-CH3C6H4
C6H5
4j
4k
4l
4-CH3OC6H4
4-ClC6H4
2-NO2C6H4
S
S
S
aAldehyde (5 mmol), urea (or thiourea) (7.5 mmol), ethyl acetoacetate (5 mmol), and 100 mg PFAMPS in
ethanol (5 ml) were heated under refux for 5 h
Scheme 3. Reaction mecha-
nism of the Biginelli reaction
catalyzed by PFAMPS
poly(2-acrylamido-2-methylpropanesulfonate) matrix in
PFAMPS was strong, and little Fe3+ was lost from PFAMPS
after reuse.
Compliance with ethical standards
Conflict of interest On behalf of all authors, the corresponding author
states that there is no confict of interest.
Acknowledgements The work was supported by National Natural Sci-
ence Foundation of China (21607085) and the Inner Mongolia Agri-
cultural University Research Initiation Funds for Doctor (BJ09-38).
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